A wide variety of coatings are available for the protection of metal alloy substrates from wear or corrosion in many environments. These coatings range from pure metallic coatings to pure ceramic coatings and encompass the cermet type of coatings which have a high volume fraction of a ceramic phase in a metal matrix. One of the most difficult environments in which to provide protection for a metal substrate is one which combines a high temperature oxidizing or sulfidizing attack with wear of a fretting or impact nature. Only a few coatings have been successful in this type of environment and virtually none when the temperature exceeds about 1800.degree. F. In the relatively low temperature range, i.e., up to 1000.degree. or 1200.degree. F., cermet coatings of tungsten carbide with a cobalt binder are commonly and very successfully used. Above this temperature, however, this type of coating is too rapidly oxidized to be useful for any extended period of time. Cermets as a general class also suffer from a lack of fatigue and impact resistance. It should also be noted tungsten carbide, in addition to being highly susceptible to oxidation, when it is exposed to hot corrosion (an accelerated sulfidation attack due to the presence of sodium sulphate or similar salts), forms a sodium tungstate which leads to a very aggressive catastrophic corrosion. In the intermediate temperature range, a coating consisting of chromium carbide in a nickel-chromium metal matrix has been used with moderate success for many years at temperatures up to about 1800.degree. F. where the wear requirements were not too severe. An example of the use of this coating is on gas turbine blade Z-notches for the older design of engines. To address the ever growing requirements for corrosion resistance and superior wear resistance of more advanced engines, a new class of coatings consisting of a dispersion of hard particles such as oxides, in relatively low volume fraction, in nickel, iron or cobalt base alloys was recently developed and is described more fully in the U.S. Pat. No. 3,864,093. For even more severe wear in corrosive environments, particularly at even higher temperature, however, this class of alloys is generally not strong enough and the matrix tends to creep under either compressive or tensile stresses.
The present invention overcomes the drawbacks associated with the coatings referred above by being directed to a composition for producing a coating for a substrate in which a matrix which is highly resistant to corrosion is strengthened by the formation of a very stable carbide or carbides, and may or may not include a dispersion of oxide particles for additional wear resistance.